How the size of a room can affect the spread of coronavirus

Considering the shop or office you're walking into is also important. You might be 6 feet away when you're speaking to someone, but if it's a small room, the accumulation droplets have only so many places to go.

Walking into the confined space of, say, your boss's office is a much different proposition than your boss walking out to speak to you in the open floor plan of your office or even outside your building.

How airflow can affect the spread of coronavirus

The amount of airflow and how it flows through an area can have a significant impact as well.

The air-conditioned, windowless restaurant offers a stark example of the dangers of sitting in close proximity to one another, as well as how contaminated air particles can stay aloft on currents within a room.

Within five days, three people sitting at the infected patron's table were infected along with another at table C – located below the air conditioner's outlet and return.

The linkage to the air conditioner and COVID-19 particles in air is more sharply drawn 12 days later. Of the 91 people in the restaurant during that hour, only those at tables A, B and C contracted the illness. There were more tables in the restaurant than shown here.

It's possible some of the patrons were infected in subsequent days by family members sitting at their table, the report notes.

Still, the close quarters and the air conditioning combined to heighten the risk that any of the patrons in that row would contract the virus. The report says, "We recommend strengthening temperature-monitoring surveillance, increasing the distance between tables, and improving ventilation."

How time can affect the spread of coronavirus

Researchers say time is another factor in whether someone contracts SARS-CoV-2. Spending a few minutes in a location rather than a few hours significantly lowers your risk of infection.

Consider the difference for those working several hours in a grocery store versus someone shopping for several minutes. Erin Bromage, an associate professor at the University of Massachusetts, points out that when the number of shoppers is restricted and the air volume in the store is large, shoppers' risk of infection is relatively low.

"But for the store worker, the extended time they spend in the store provides a greater opportunity to receive the infectious dose, and therefore, the job becomes more risky," Bromage wrote in his COVID-19 blog.

Nearly 100 people contracted COVID-19 on one floor of the building that housed the call center. The building's infection rate was 8.5%, but the call center's infection rate was as high as 43.5%, according to the report. Even more unusual: All but five of the reported cases were on one side of the floor.

The close proximity of the workers' desks contributed to some of the spread, the CDC report says, but the fact that the spread was limited to one part of the call center suggests more was at work:

"Despite considerable interaction between workers on different floors of building X in the elevators and lobby, spread of COVID-19 was limited almost exclusively to the 11th floor, which indicates that the duration of interaction (or contact) was likely the main facilitator for further spreading of SARS-CoV-2."

Closer to home, a choir practice March 10 in Washington state appears to have been the focal point of dozens of infections (including two deaths). After more than two hours singing in a room about the size of volleyball court, "deep-breathing while singing facilitated those respiratory droplets getting deep into the lungs," Bromage wrote.